M-b-335: Break to Atmosphere Twin Tanks
200 C Street, SW
Washington DC 20204
November 30, 2001
TO: All Regional Food and Drug Directors
Attn: Regional Milk Specialists
FROM: Milk Safety Team (HFS-626)
SUBJECT: Break to Atmosphere Twin Tanks
The Break to Atmosphere Twin Tanks has been reviewed and found to comply with the applicable provisions of the Grade A Pasteurized Milk Ordinance (PMO) when used as an atmospheric break between raw and pasteurized milk and milk products.
Compliance with the PMO is based upon construction, installation and operation in conformance with the attached drawing and operating description as well as the following criteria from the NCIMS Technical Committee, addressed in the solution to Proposal 119, passed at the 2001 NCIMS Conference:
The distance between the overflow level of the lower balance tank and the outlet of the outlet control valve on the upper balance tank must be the greater of the liquid column height of the lower balance tank plus two times the diameter of the pipeline connecting the upper and lower balance tanks or 28 inches plus two times the diameter of the pipeline connecting the upper and lower balance tanks. Additionally, the plug on the control valve shall be grooved to prevent complete closure of the valve.
For further information contact:
Warren Taylor Services, Inc.
37444 Holley Road
Pomeroy, Ohio 45769
Phone: (740) 992-7992
Fax: (740) 992-7994
FDA's review and acceptance of this equipment, does not constitute agency endorsement or approval. Any representation on a label or in printed literature citing or indicating as, "FDA Approved" is false and misleading.
Copies of this memorandum are enclosed for distribution to Regional Milk Specialists, State Milk Regulatory Agencies and State Milk Sanitation Rating Officers in your region. This memorandum will also be available on the FDA Web site at http://www.cfsan.fda.gov at a later date and should be widely distributed to representatives of the dairy industry and other interested parties.
Steven T. Sims FDA/MST Milk Sanitation Officer
WARREN TAYLOR SERVICES, INC.
37444 Holley Road Pomeroy, Ohio 45769 USA
Tel:(740)992-7992 Fax: 992-7994 E-mail: WTSPRO@aol.com
November 1, 2001
Break To Atmosphere Twin Tanks
The Problem - To provide absolute separation of pasteurized product and product contact surfaces, such as HTST systems and discharge piping, from raw product, piping, and equipment, to which pasteurized product must be transferred.
By regulatory code this requires a break to atmosphere, which has typically been met by providing a tank in which the inlet drops product well above the product level. The resulting splash and turbulence of product and air causes foaming, particularly when skim milk is transferred.
Foaming lends to numerous problems including product loss, poor homogenization efficiencies, burn on in HTST plates during reprocessing, and increased temperatures and microbiological activity.
The Solution - A unique Twin Break Tank arrangement in which pasteurized product is bottom fed into an elevated HTST type balance tank ("Top Tank") and allowed to flow by gravity into a similar lower balance tank ("Bottom Tank"), again bottom fed.
Since both tanks are vented vessels which are constructed so they cannot be pressurized or under vacuum, it is not possible for raw product to back feed under pressure beyond the bottom tank overflow opening. It is also not possible for raw product to be drawn by vacuum up into the top tank. In this way, raw product cannot possibly migrate back to the pasteurized side and contaminate pasteurized product or product contact surfaces. At the same time, pasteurized product transferred to the raw side through the Break Tank(s) is bottom filled into each tank, minimizing product/air mixing and foaming problems.
The Details - Refer to the attached drawings 2029-01, 02, 03, 04, 05, 06 and 07 which show the system requirements and operation.
Overview - The system can be piped into an existing operation. Its controls are best integrated with the existing HTST and raw destination tank controls to reduce the possibility of product loss due to HTST recycle or divert, or raw destination tanks overflowing. This also makes it possible to provide automatic Break Tank emptying and associated line air blowing to minimize product losses, and automatic CIP sequencing to assure consistent cleaning.
A self contained control system can be provided for integration with existing controls or in the case of facilities with computer or programmable controller type controls, the existing plant control system can be used to provide the necessary automation.
Level is maintained in Break Tanks above the side inlet level to prevent foaming. Level is controlled in the top tank by modulating the control valve between the tanks. Level is maintained in the bottom tank by controlling the rate that product is pumped away by the removal pump. This can be done either with a throttling valve on the removal pump discharge or by controlling the motor speed with a variable frequency drive.
Operational Control Description - There are three distinct modes of operation:
Process Mode - The Break Tanks are empty following CIP cleaning until product is introduced into them. When product is first introduced, the level controllers act to fill the tanks, not operating the removal pump and holding the control valve closed. Once the top tank level reaches setpoint, the control valve will begin to open, dropping product down to the bottom tank until the setpoint level is reached there. The removal pump will then start, pumping product out at the same rate it is entering the Break Tanks.
This operation will continue until the transfer is completed. At that time an automatic or manually initiated pumpdown/airblow sequence can operate to thoroughly empty both Break Tanks and the transfer lines.
Pumpdown/Airblow Mode - After the transfer is completed, as indicated by the closure of the HTST discharge valve to the Break Tank, the level control of the top tank is stopped to allow the control valve to open and allow all product to flow to the bottom tank. After a preset time which will be determined by the particular plant's HTST discharge piping, the HTST discharge airblow can be activated to purge the line of product to the top tank.
The control valve will remain open so the top tank will be allowed to completely drain.
The removal pump continues to operate under level control, maintaining setpoint level. Once the top tank is empty the level control of the bottom tank is stopped with the removal pump operating for an adjustable time delay after the bottom tank has reached low level.
The bottom tank outlet valve airblow is then activated in combination with the other plant valves on the way to the destination tank(s) to purge the transfer lines.
CIP Mode - The Break Tanks can be cleaned in a line circuit with flow rates in the range of 80 to 140 GPM, or in a dedicated Break Tank circuit. The CIP supply valves are cycled to spray the tanks during part of the circuit, with flow also cycled through the normal product piping. At the end of the cycle the tanks are pumped down, as in a typical tank CIP cycle.
Level Controls - The Break Tank level controls for each tank are similar in operating modes and functions. Both tanks are equipped with analog level sensors which may be pneumatic diaphragm, electronic pressure sensor, or capacitance type. There are two discrete alarm setpoints ("low" and "high") in addition to the "operating level setpoint".
System operating responses are listed below.
Top Tank & System Response
High Level (about 24") Process: Stop the source, typically recycle the HTST. Pumpdown/Airblow: Stop the source airblow. CIP: None.
Operate Level (about 12") Process: Control valve modulated to maintain. Pumpdown/Airblow: None. CIP: none
Low Level Process: None. Pumpdown/Airblow: None. CIP: none
Bottom Tank & System Response
High Level (about 24")
Process: Close the control valve and sound alarm.
Pumpdown/Airblow: Close the balance valve until high level signal is lost.
CIP: None, except sound alarm.
Operate Level (about 12")
Process: Removal pump rate modulated to maintain.
CIP: Removal pump rate modulated to maintain.
Process: Stop removal pump and close bottom tank outlet valve.
Pumpdown/Airblow: Start the time delay before closing the bottom tank outlet valve and starting the airblow.
CIP: Stop the removal pump and close the bottom tank outlet valve.
Specific Installation Variations - Variations of tank sizes, piping configurations, and controls are possible as long as the basic principals of the system are maintained.